The processing of photosensitive material involves a series of steps such as developing, bleaching, fixing, washing, and drying. These steps lend themselves to mechanization by conveying a continuous web of film or cut sheets of film or photographic paper sequentially through a series of stations or tanks, each one containing a different processing liquid appropriate to the process step at that station.
There are various sizes of photographic film processing apparatus, i.e., large photofinishing apparatus and microlabs. A large photofinishing apparatus utilizes tanks that contain approximately 100 liters of each processing solution. A small photofinishing apparatus or microlab utilizes tanks that may contain less than 10 liters of processing solution.
The chemicals contained in the processing solution: cost money to purchase; change in activity and are seasoned by the constituents of the photosensitive material that leach out during the photographic process; and after the chemicals are used the chemicals must be disposed of in an environmentally safe manner. Thus, it is important in all sizes of photofinishing apparatus to reduce the volume of processing solution. The prior arts suggest various types of replenishing systems that add or subtract specific chemicals to the processing solution to maintain a consistency of photographic characteristics in the material developed. Photosensitive material processing equipment typically consists of several large volume tanks of processing solution that the exposed photosensitive material is driven or towed through to produce an image, as the photosensitive material is processed the strength of the processing solutions is diminished and will eventually become exhausted. To prevent the continual weakening of the processing solution additional fresh processing solution is added to the tank solution at a rate equivalent to the rate of use and rate of carry out of the processing solution. The above maintains processing solution activity and volume. Typically the replenish is very small compared to the working processing tank volume. A typical ratio of replenishment per square foot of photosensitive material for a large volume tank would be 0.00025 to 0.00075 of the tank volume. Since the above ratio is small the effect of pulsing delivery and cyclic variation of the replenishment delivery by 5 or 10% over time, does not have an immediate significant effect on the processing solution.
Typical replenishment is accomplished by using a single standard bellow pump (like Gorman-Rupp single bellow metering pump mode number 13300-007). When replenishment is required the pump is turned on/off through known means and the replenishment solution is pumped in "doses" or "squirts" usually into the top of the main processing tank in close proximity to the recirculation system. As the bellows pump delivers solution to the top of the tank, the bellows pump is not experiencing any variable back pressure or head. As the replenishment in the large tank occurs, the pressure is only that of line restriction and gravity from the replenishment storage tanks to the solution delivery location. The pulsing delivery is acceptable as the ratio of replenishment to tank solution is very small. The above pump works well for large volume tanks, because the large volume of solution acts as a ballast.
Replenishment calibration is typically a manual operation involving running the replenishment pump and measuring the solution output volume. This measuring device used is most often a graduated cylinder. The measured amount of solution is compared to the chemical manufacturers' specification for the type of photosensitive material and amount of replenishment solution required to be added.
Successive timed measurements of replenishment solution delivery are made to determine the actual replenishment solution delivery rate. If adjustments are required, a manual adjustment of the bellows pump is made. Following the adjustment, the delivery of replenishment solution is again measured, and further adjustments are made until the delivery of replenishment solution is consistently at the required amount. During the above adjustment time the processor can not be used to process photosensitive materials. Thus, the processor would not be processing photosensitive materials when the pumps are being calibrated.